1. Field of the Application
The present invention relates to processes for the preparation of metal carbides and, more specifically, to a process for preparing titanium carbide which is useful as an abrasive, refractory and wear-resistant material in ferrous and non-ferrous metallurgy.
2. Description of the Prior Art
A process for preparing titanium carbide by reducing titanium dioxide with carbon in a protective atmosphere (hydrogen, carbon dioxide or methane) in high-temperature furnaces at a temperature within the range of from 1,700.degree. to 2,100.degree. C. is known in the art. To increase the content of carbon, titanium carbide is repeatedly heated with carbon.
However this process suffers from a disadvantage residing in the need to employ sophisticated power-consuming equipment, the productivity of the process equipment is low (not more than 0.5 kg/hr per one graphite-tubular furnace), and the quality of the final product is poor (the content of bound carbon being 18.0-19.5% by weight, content of free carbon 1.0 to 2.5% by weight the stoichiometric content of bound carbon being 20.0% by weight).
There is also known in the art a process for producing high-melting compounds of carbides, nitrides and borides of metals belonging to Groups IV, V and VI of the periodic system.
This process comprises mixing at least one of the above mentioned metals in equimolar ratio with one of the non-metals such as carbon, boron, nitrogen and silicon. The resulting mixture is placed in a reaction vessel which is filled with an inert gas, the reaction vessel volume substantially exceeding the volume of the reaction mixture. Then, a local heating of a small region of the reaction mixture surface area is effected by means of a heat source. As a result, a combustion process is initiated in a thin layer of the mixture of the starting components which self-propagates over the entire reaction mass. This self-propagation of combustion over the reaction mass occurs owing to the heat released in the reaction of the starting components and to the heat-transfer process. The combustion zone has a temperature within the range of from 2,500.degree. to 4,000.degree. C.
A disadvantage of this prior art process resides in the necessity of using high-grade starting components. Thus, in the case of powder-like titanium contaminated with oxygen, hydrogen, nitrogen and chlorine, gaseous by-products are formed during the synthesis of titanium carbide which cause scattering of the reaction mass. The reaction becomes uncontrollable. To prevent the reaction mass from scattering, is is necessary to perform the process in an inert gas atmosphere under a pressure ranging from dozens to hundreds of atmospheres. Furthermore, the presence of gaseous impurities upon cooling of the resulting titanium carbide causes contamination thereof and, hence, impaired performance characteristics of the final product, e.g. abrasive properties.
Another disadvantage of the afore-described prior art process resides in the impossibility of producing titanium carbide on a commercial scale.